Microtubules are ubiquitous cellular structures that perform diverse structural and developmental functions in all eukaryotic organisms. In D. melanogaster, the primary components of microtubules, Alpha- and Beta-tubulins, are encoded by small families of developmentally regulated genes. Two Alpha- and 2 Beta-tubulin proteins, and 4 Alpha and 4 Beta coding sequences, have been identified, but only one protein has been unequivocally matched with its gene. We propose to analyze the genetics of tubulin in this eukaryote with the goal of understanding how these two families of developmentally important genes participate in the morphogenic process. We will examine: 1) the structural contribution of these genes to development (do all the tubulin genes make proteins, are they structure specific?); 2) the regulation of these genes during development (which proteins appear where and when?); and 3) the regulatory contribution of these genes to development (if a tubulin is structure specific, does its appearance trigger the production of that structure?). We will address all of these questions with a combined genetic and molecular approach, including mutational and gene dosage studies, analysis of the protein products, and analysis of the DNA and RNAs of the various tubulin loci in mutant and normal individuals. The notable lack of success of the many attempts to recover regulatory mutations in Drosophila has lead us to consider alternative approaches to the study of gene regulation. An investigation of the regulation of tubulin production from an evolutionary perspective will be undertaken. We will determine whether other species of Drosophila have the same repertoire of tubulin genes, and investigate the temporal and spatial patterns of expression of these genes. Homologous tubulin genes with developmental regulation differing from that in melanogaster can be examined at the molecular level for differences in structure. The ability of homologous tubulin genes from another Drosophila species to be properly regulated in melanogaster cells will be examined using the P factor-mediated transformation technique; we will attempt to complement melanogaster tubulin mutations with homologous genes from other species. Comparisons of the orgnization, structure, and regulation of tubulin genes among different but functional systems has the potential for providing new insight into the mechanisms of eucaryotic gene regulations.